tie is a link command that is used to "tie" the two turtles at the ends of the links together, almost like the two turtles were attached with a perfectly rigid length of steel. If the link is directed, then the to turtle follows the from turtle but not the other way around. If the link is undirected, then both turtles will try to mimic the movements of the other, which can often become slightly chaotic. A tied turtle will not only follow the movement of the other, but also will also pivot around the rotating turtle when it turns and copy its new heading.

Because tie is a link command, it needs to be executed within a link context, such as ask links [tie] or, more commonly, create-links-to turtles [tie]. Note that since the tie is applied to the link, when the link is destroyed or either of the turtles at the ends die, the tie is destroyed as well.

In this model, we use tie to model the symbiotic relationship between whales and whale barnacles. In this relationship, the whale barnacles attach themselves to whales as they swim around. Since these barnacles passively filter food from the ocean water, it is highly beneficial for them to hitch a ride with these fast moving whales as they travel through the ocean. To model this attachment, we use tie along with a directed link to make the barnacles, once attached, follow the whales movement.